It might help to wipe the cache partition, which is a system cache of temporary data. Wiping it doesn't erase any important data, but might correct a glitch like this. Steps are:
1. Turn off the device.
2. Press and hold the following three buttons at the same time: Volume Up key, Home key, Power key.
3. When the phone vibrates, release the Power key but continue to press and hold the Volume Up key and the Home key.
4. When the Android System Recovery screen appears, release the Volume Up and Home keys.
5. Press Volume Down until Wipe Cache Partition is highlighted, then press Power.
6. When the wipe is done, select Reboot System Now.